Real gas is a physical gas whose behavior reflects the actual properties of its molecules, including finite molecular size and intermolecular forces such as attraction and repulsion. Unlike an ideal gas, a real gas does not obey the ideal gas law exactly under all conditions, particularly at high pressures or low temperatures where molecular interactions and volume become significant. To accurately describe real gas behavior, more complex equations of state, such as the Van der Waals, Redlich–Kwong, Soave–Redlich–Kwong, or Peng–Robinson equations are used. Real gas behavior explains phenomena like gas liquefaction and deviations in pressure–volume–temperature relationships, and it is essential for precise modeling in thermodynamics, chemical engineering, and fluid flow applications.
There is no special subset called “real gases,” all gases that exist in nature are real gases because they all have finite molecular size and intermolecular forces. That said, here is a list of common real gases typically referenced in engineering, physics, and chemistry: Air (Gas Mixture), Ammonia, Argon, Butane, Carbon Dioxide, Carbon Monoxide, Chlorine, Ethane, Helium, Hydrogen, Krypton, Methane, Nitrogen, Nitrous Oxide, Neon, Oxygen, Propane, Sulfur Dioxide, Water Vapor, Xenon, etc.
In practice, gases like helium, hydrogen, nitrogen and air are often treated as ideal gases under normal conditions, but they are still real gases and will deviate from ideal behavior at high pressure or low temperatur
